With the continued increase in oilfield operations with demanding service conditions, mainly characterized by high temperature (HT) and extreme corrosive environments like those containing large halide concentrations and/or corrosive gases like CO2 and H2S, the reliability and service life of downhole equipment is significantly affected. Downhole fluids such as drilling, completion, production, and stimulation fluids might be detrimental to the integrity of the majority of materials used in subsurface engineering equipment. Materials degradation mechanisms in aqueous environments including corrosion strongly depend upon chemical speciation, pH and temperature of the environment. It is well known that acidic conditions (defined herein as a pH equal to or less than 6) may increase dramatically the corrosion susceptibility of metallic materials including cemented tungsten carbides, steels, aluminum, copper and cobalt alloys.
In further detail, downhole fluids might contain large concentrations of halides such as chlorides or bromides. Alternatively or additionally, these fluids might become contaminated with corrosive gases like H2S and CO2. Having low pH, these fluids can, therefore, be very detrimental to different materials. On the other hand, it has been proven that high pH reduces significantly the corrosion susceptibility of metallic materials when exposed to high-salinity and H2S-bearing downhole environments. To address this problem, corrosion inhibitors and scavengers are routinely added to the oilfield fluids to reduce or prevent the corrosion caused by dissolved acidic gases. However, continuous corrosion control via chemical treatment (inhibitor injection) during production is very costly. On the other hand, the dosing of inhibitors and pH-adjustment controlled by sporadic measurements on the surface introduces a time delay that reduces the effectiveness of the corrosion inhibitors. Additionally, corrosion inhibitors injected from the surface can be diluted during transportation to the area in the wellbore where increased corrosion inhibition is necessary. Therefore, these conventional methods increase the risk of failure due to quick unforeseen excursions from the operational window.
It would thus be desirable to provide methods and apparatus to that could increase the inhibition and/or prevention of corrosion in-situ when and as needed downhole.